Method for rotational molding



April 7, 1970 A. c. EICHMANN ET AL 3,505,437

METHOD FOR ROTATIONAL MOLDING Original Filed April 26, 1963 2Sheets-Sheet 1 Fig. 4

INVENTORS ALBERT C. EICHMANN CARL A. DAMN JOHN R. HESS RALPH L.McGIBONEY April 7, 1970 A. c. EICHMANN ET AL METHOD FOR ROTATIONALMOLDING 2 Sheets-Sheet 2 Original Filed April 26, 1963 INVENTORS ALBERTC. EICHMANN CARL A. DAMM JOHN R. HESS RALPH L. MOGIBONEY United StatesPatent 3,505,437 METHOD FOR ROTATIONAL MOLDING Albert C. Eichmann,Bethayres, Carl A. Damm, Upper Black Eddy, John R. Hess, Oreland, andRalph L. Mc- Giboney, Prospectville, Pa., assignors to the United Statesof America as represented by the Secretary of the Navy Originalapplication Apr.. 26, 1963, Ser. No. 276,112, now Patent No. 3,341,236,dated Sept. 12, 1967. Divided and this application July 17, 1967, Ser.No. 654,011

Int. 'Cl. B29h 9/10; B32b 15/ 06'; B29d 27/04 US. Cl. 264-45 1 ClaimABSTRACT OF THE DISCLOSURE A rotatable, annular assembly of spaced apartmetallic sprags which are bonded together by a polyurethane elastomerand method and apparatus for making the assembly. The annularly arrangedsprags, which are spaced apart by a notched spacer ring, are positionedin a centrifugal mold. The elastomer is introduced thereinto in a fluidstate for one embodiment and in a foamed state for another. The mold isspun in a curing oven.

This is a division of application Ser. No. 276,112 filed Apr. 26, 1963,now US. Patent 3,341,236 issued Sept. 12, 1967. x

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

The present invention relates to the manufacture of a molded compositearticle and more particularly to the manufacture of a centrifugally-castmolded article.

Known article retaining structures, such as ball-detents and claws arecharacterized by providing a relatively small area of contact with thearticle to be retained in proportion to the size of the retainingstructure and the number of retaining elements provided therein.Further, since the surface of the retained article engaged by theretaining members and the surface of the reaction member, asconventionally provided, are substantially in line in prior art devices,wearing of parts soon reduces the effectiveness of these devices.

The arrangement described in US. Patent No. 3,043,- 614 is an attempt toobviate the above-noted deleterious condition by the formation thereofof an annular sprag assembly wherein the interstices between a pluralityof metallic sprags having a semicircular body portion and opposedsemicircular lip portions are partially filled with a flexible materialhaving good surface characteristics, such as polyurethane. However, thisstructure was found to provide an unsatisfactory bond between theflexible material and the metallic sprags. Additionally, when theassembly moved between the opened and closed position thereof, theflexible material was significantly extruded outwardly beyond theexterior limits of the sprags with attendant friction problems ofserious dimension. This factor obviously also decreased the life of thematerial between the sprags.

It is, therefore, an object of the present invention to overcome theabove-noted and other disadvantages of the prior art and to provide amethod of making a simple, compact, inexpensive and reliable mechanicalcoupling element.

Another object of the present invention is to provide a method of makinga molded sprag assembly which is a bonded unit and one which issusceptible to mass production techniques.

An additional object of this invention is to provide a method formolding an annular assembly comprised of a plurality of metallic spragsand flexible material therebetween.

A still further object of the present invention is to provide a methodfor manufacturing an annular ring assembly, which method and apparatusis readily adjustable for providing annular ring assemblies of varyingmuscle or rotational force resistance.

Various other objects and advantages will appear from the followingdescription of the several embodiments of the invention, and the mostnovel features will be particularly pointed out hereinafter inconnection with the appended claim.

In the drawings:

FIG. 1 shows a plan view of the sprag assembly.

FIG. 2 illustrates an enlarged section taken along line 22 of FIG. 1showing one sprag.

FIG. 3 illustrates a plan view of the sprags and retaining ring prior tointroduction within the mold.

FIG. 4 illustrates a vertical cross-sectional view of one embodiment ofthe centrifugal mold with a portion of the core broken away for purposesof further clarity.

FIG. 5 is a view similar to that taken along the line 22 of FIG. 1illustrating a second embodiment of the invention.

FIG. 6 is a vertical cross-sectional view of a second embodiment of themold for producing the sprag assembly as shown in FIG. 5.

The sprag assembly, generally noted at 10 in FIGS. 1 and 2, is anannular structure which may be used in a mechanical coupling apparatusas shown, for example, in the US. Patent No. 3,043,614.

Referring to FIGS. 1 and 2, it will be seen that the sprag assembly 10comprises a plurality of sprags 11 of metal or other suitable material,each of which, referring particularly to FIG. 2, has a semicircular bodyportion 12 of radius R, terminating in opposed semicircular lip portions13, 14 of radii R the lip portions 13 forming the mouth of the assembly10. The interstices between the sprags are partially filled bywedge-shaped, truncated arcuate segments 15 of a flexible and elasticmaterial having good surface bonding characteristics, such as anelastomer of polyurethane or the like, to form a generally annularassembly wherein sprags 11 are free to rotate to a limited extent aboutan annular axis A.

In order to insure that each sprag 11 has the lip portion 13 thereofengaging the appropriate abutting surface of the connector, not shown,such as for example, the groove 11 of the lock-on stud of Patent No.3,043,614, the annular'assembly 10 is formed with a thin elastic coatingor cushion 16 of the elastomer which abuts the retaining surface, notshown, when the assembly 10 is placed into its operative position. Inaddition, the annular coating 16 is formed integrally with the segments15 and thereby provides the segments with reinforcement in the inboardarea subjected to the greatest stretching and stress.

As is clearly seen in FIG. 2, each sprag 11 includes an aperture 17 atthe bisecting center line or neutral axis N thereof which passes throughthe annular axis A and which is filled with the elastomer to form anintegral locking lug 18. By virtue of the totality of apertures 17 andlugs 18, the completed sprag assembly 10 is reinforced by the continuityof elastomer throughout the entire ring, thereby reducing the necessityof utilizing a strong bonding agent for joining the sprags and flexiblematerial. Also, by placing the apertures 17 on the neutral axis N andnear the outer perimeter of the sprags 11, the ring formed by the lugs18 is subjected to the least possible stresses when the assembly 10 isflexed in the operation thereof. It is further contemplated by thisinvention that an annular spring element, not shown, may be provided toextend through the aperture 17 to obtain an additional mechanical bond.

In order to preclude the extrusion of the flexible material beyond theconfines of the assembly when the same is rotated about the annular axisbetween the opened and closed position, the truncated arcuate segmenthas the planar outer surface 19 thereof forming a cavity with theadjacent sides of the sprags 11 into which the material of the segment15 may extmde. This cavity also provides a housing for the oil or otherappropriate material utilized in lubricating the assembly 10 in theoperation thereof.

Although the lip portions 13-14 are illustrated as having a semicircularconfiguration, it is contemplated by this invention that the engagingedges of the lower lips may be flattened to eliminate point contact andto provide a greater bearing surface.

With reference to FIGS. 1, 2 and 4, it is seen that the sprag assemblyis constructed with the upper lip portions 13 separated from each otherthereby forming a normally open mouth or aperture 21, and isadditionally constructed with the lower lip portions 14 in abuttingrelationship thereby forming a normally closed aperture 22. It isfurther seen that the segment 15 has the outboard planar surface 19 andinboard planar surface 23 thereof positioned normal to a radial linefrom the polar or longitudinal axis in the plane of the annular axis Aof the assembly 10. This attitude is important for the proper mechanicalfunctioning of the assembly whereby the mouth 21 returns to the normallyopen position, as illustrated in FIG. 1, after having been urged to theclosed or locking position wherein the lip portions 13 were in abuttingrelationship.

The method and apparatus for constructing the sprag assembly 10 will nowbe described with reference to FIGS. 3 and 4 which illustrate,generally, spacer ring 25, mold core member 30 and centrifugal mold 40.The spacer ring 25 is of annular configuration and includes an innercircumferential face 26 having a plurality of notches 27, equal to thenumber of sprags 11 in the assembly 10, formed therein. The ring 25 andthe face 26 thereof, thereby, not only position the sprags 11 in thenotches 27, but also provide, between the sprags 11, the outboardconfine for the elastomer and permit the formation of the cavities 20into which the extruded material flows.

In the assembly of the sprags 11 prior to the introduction thereof intothe mold 40, the core member 30 is placed vertically in an assembly jigknown to those skilled in the art, and not shown, which includes aplurality of slots for vertically and circumferentially positioning thesprags 11. After the sprags are placed into the abovementioned slots andseated against the core 30, the spacer ring 25 is lowered over theassembled sprags and assumes a horizontally central position about theassembly. The sprag-spacer ring-core arrangement, illustrated in FIG. 3,is then separated from the jig and interposed within the mold 40, asshown in FIG. 4.

Referring now more particularly to FIG. 4, it is seen that the coremember 30 comprises an integral shaft 31 secured to the mold 40 by keys32 and an upper core portion 33 having a longitudinal bore 35 extendingpartially therethrough. Extending 90 to each other and communicatingwith the bore 35 are a pair of radial ports 36 for supplying theelastomer in its fluid state to the assembled sprags 11. Circumferentialshoulder portions 37 are formed in the upper core portion 33 and areangularly related to the longitudinal axis of the core 30 to obtain anabutting relationship of the lip portions 14 and also to thereby obtainan assembly 10 having a normally opened aperture or mouth 21.

Referring again to FIG. 4, the centrifugal mold 40 comprises an uppermold section 41 and a lower mold section 42 jointed together byfasteners 43. Each of the sections 41-42 are constructed with abuttingbases 44 each having circumferential grooves 46 formed therein forreceiving and housing a portion of the spacer ring 25. Arcuately-shapedcircumferential grooves 48, generally conforming to the radius R of thesprag 11, are additionally formed in the upper and lower sections 41-42for loose engagement with the semicircular body portions 12 of thesprags 11, which thereby permits the formation of the cushion or coating16.

The upper section 41 also includes an axial shaft member 51 having amaterial inlet opening 52v extending therethrough and communicating withthe longitudinal bore 35 in the core member 30.

As illustrated in FIG. 4, the mold as above described in assembled formis attached by shaft 31, through coupling S3, to a motor shaft 54 whichis part of a temperature-controlled curing oven and spinning fixture(not shown), the motor being capable of rotating the mold at a speednecessary to produce the desired centrifugal force. The axial shaftmember 51 is rotatably secured to the curing and spinning fixture bybearings 56 suitable secured to the frame 57 of the fixture.

Before the mold is spun, the curing oven is preheated and a meteredquantity of polyurethane mixture in its liquid state is introduced by ahypodermic syringe directly into the middle section of the mold. Inseeking its own level, the liquid polyurethane mixture passes throughports 36 and is distributed equally in all the voids existing betweenthe sprags 11. As the mixture fills in, the displaced air rises throughthe space between the needle of the syringe and the inlet opening 52 andescapes the confines of the mold. The curing temperature and length ofspinning time is then set in accordance with the specific formulation ofthe material inserted, and in accordance with the desired density ormuscle of the flexible segments 15. When the mold spins, the material isdriven by the centrifugal force into the voids between the sprags 11thereby forming segments 15 and into the grooves 48 between the spragedges and the mold thereby forming coating 16. When the spinning andcuring process has been completed, the finished article shown by FIG. 1may be removed from the mold.

A second embodiment of the invention is seen with particular referenceto FIGS. 5 and 6. This embodiment utilizes an elastomer, such aspolyurethane, in a foam form, which upon setting becomes rigidelastomeric foam. By reason of this variation in material used and otherfactors discussed below, the process produces segments 15, shown in FIG.5, which difier from segments 15 in that they vary in density from theinboard to the outboard edge of the sprag 11', with the inboard portion58 having the least density and the outboard portion 59 having thegreatest density. It is therefore seen that an assembly is constructedwherein the area of the segment subjected to the greatest tensilestresses is formed with elastomer of the least density, that is, themost easily stretched without rupture. This is obtained withoutabandoning the desired muscle or spring force and without abandoning thebonding strength obtained by the elastomer wetting the surface area ofthe sprags 11.

In order to obtain the variable density segment 15', thesprag-core-spacer ring assembly is interposed within the mold, generallynoted at 60. The mold 60 comprises upper and lower mold sections 61 and62, respectively, the upper section 61 having a funnel-shaped egressport 63 formed therein to offer interior mold surface up to the inneredge of the required elastomer fill.

The core member 65 has an enlarged longitudinal bore 66 at one endthereof for receiving the poured elastomer foam and radial ports 36 fordistributing the same to the interstices between the sprags.

For purpose of regulating the thickness of the coating or cushion 16',the integral shaft 67 of the core member 65 has a threaded portion 68engaged by adjusting nut 69 which in turn abuts the lower mold section62. It is readily seen, therefore, that the rotation of the nut 69 willmove the core 65 and abutting sprags 11 thereby regulating the width ofthe arcuately-shaped groove 70 formed between the assembled sprags 11and the mold sections 6162.

In the formation of the second embodiment sprag assembly, thesprag-core-spacer ring assembly is interposed within the mold 60 and themold placed in the temperature-controlled spinning fixture in a mannersimilar to that discussed above with relation to the first embodiment.An indiscriminate amount of elastomer foam is then poured into the coremember 65, the elastomer distributing itself evenly through all thespaces. When the mold is spun in the fixture, any excess material isdriven off at the edge of the desired fill through the egress port 63.

The density variation of the segment 15' is controlled by thecentrifugal force obtained by the spinning of the mold 60 within theabove-mentioned fixture, the formulation of the elastomer foam, thetemperature to which the mold is exposed and the time of exposure of themold to this temperature.

What is claimed is:

1. A process for molding an array of similarly configured planar spragelements into an integral assembly in which the sprag elements arecollectively rotatable about an annular axis, said process comprisingthe steps of:

juxtaposing the planar sprag elements at intervals about a core memberhaving an axis so that an edge of each abuts the core member, therebeing an interstice between each sprag element and the adjacent spragelement;

encircling the juxtaposed sprag elements with an an nular spacer ringfor maintaining the relative positions of the elements;

placing the encircled sprag elements and core member within a moldhaving a relief configuration of the encircled sprag elements;

spinning the mold and its contents about the core axis;

introducing a greater amount of fiowable elastomer foam into each of theinterstices between adjacent sprag elements than is required to make adesired fill;

controlling the radial outermost points at which excess elastomer foamiss pilled out during said spinning step, said spinning step occurringat a speed to produce a centrifugal force to establish truncatedsegments of elastomer of radially varying density forming a segmentedcylindrical interior elastomer boundary which extends parallel to theaxis, which is positioned radially outwardly of the core adjacent edgesof the sprag elements and through which protrude the core abutted edgesof the sprag elements; and

curing the foam remaining in the interstices during said spinning stepto solidify said truncated segments of elastomer of radially varyingdensity.

References Cited UNITED STATES PATENTS 2,671,932 3/1954 Pique 264-311 XROBERT F. WHITE, Primary Examiner I H. SILBAUGI-I, Assistant ExaminerUS. Cl. X.R.

